There is known to exist in the prior art numerous different methods and a wide variety of dynamoelectric machine structures that are designed to be useful in reducing vibration that is created by the operation of such machines. Such prior art methods and apparatus structures are distinguished from the present invention by their respective characteristic features, but in general they differ from the present invention by being designed to be primarily useful in coping with the problems of vibration in a finished machine, rather than being designed and useful in the prevention of the causes of such vibration at the time the machine is manufactured, as is the case with the present invention. Some examples of such vibration-damping structures and methods are shown in U.S. Pat. Nos. 4,204,313; 2,846,630; 2,811,659 and 2,720,600, each of which discloses either undercut, axially extending, stator-core-supporting resilient ribs, or undercut resilient housing ribs having portions that engage axially extending bars on the respective illustrated stator cores. Such undercut rib portions are made sufficiently resilient (or are arranged so they are not stressed beyond their inherent elasticity) to absorb much of the vibration that may be induced in a stator core during its operation, but in none of the disclosed cases does it appear that the under-cutting is either designed to, or in fact serves to, reduce the causes of such vibration. For example, none of these disclosed cases appear to suggest ways of making the air gap between a rotor and stator of such a machine more uniform over its circumference.
A somewhat similar type of vibration damping function is commonly provided in various known prior art types of dynamoelectric machine structures by a variety of snubber or torsion bar arrangements that are typically disposed between a stator core and a surrounding support housing to limit the amount of vibration that can be transmitted from the core to the housing during normal operation of a machine. For example, U.S. Pat. Nos. 3,708,707; 2,973,442; 3,772,542 and 2,953,697 disclose various forms of resilient snubbers or spring leaf members that are mounted in either tension or compression between a stator core and relatively rigid portions of a surrounding housing to effect such vibration damping.
U.S. Pat. Nos. 2,754,441 and 4,060,744 further disclose the use of torsion bar support arrangements mounted between stator cores and adjacent housing ribs of a surrounding rigid housing. Such torsion bar arrangements are similar to the other known prior art anti-vibration mounting means in that they are operable to accommodate vibration induced in a stator, but they are not effective to remove the causes of such vibration at the time the machine is manufactured.
It is also known in the prior art to provide rigid stator core mounting arrangements that enable the core position to be adjusted relative to a supporting housing, thereby to provide a more precise and uniform air gap between the stator and an associated rotor. U.S. Pat. No. 3,519,857, for example, discloses such a rigid stator core support means in which a plurality of adjustable fasteners are used to selectively apply pressure to different points around the periphery of a stator, thereby to accurately position it relative to a desired axis of rotation through the housing, which may be eccentric to the main central axis of the housing, but which would correspond exactly with a desired axis of rotation of an associated rotor. A common feature of this patent and the other prior art patents mentioned above, is that its core positioning means and the vibration damping snubbers or undercut portions disclosed in the other patents are distributed at equiangular points around a stator core in order to provide uniformly distributed pressure to the core around its circumference. Thus, in practice, such known prior art structures and vibration-dampening methods are not effective to counteract or avoid the application of unequal pressures being applied at different points to a stator core by portions of a surrounding stator support housing that have different degrees of radial rigidity. Accordingly, such known prior art structures and methods are not useful for preventing a stator core from being distorted into an out-of-round configuration by the forces transmitted to it from surrounding housing ribs into which the core is thermally shrunk-fit.
Finally, it is known in the prior art, as disclosed in U.S. Pat. No. 4,145,626, to mount a stator core in a core-supporting housing by positioning a plurality of axially extending ribs around the stator core between it and annular ribs of the supporting housing. In that patent, in order to provide relatively uniform stressing of each of the supporting ribs, only those supporting ribs adjacent the most rigid portions of the surrounding annular ribs of the housing are made resilient by undercutting the ribs. The remainder of the ribs, i.e., those at the upper and lower portions of the surrounding housing, are not undercut, therefore, the possibility of stress-relieving those ribs in response to either radial distortions of the stator core caused by different distributions in the core weight or by electrodynamic forces applied to the core during operation of the machine, are substantially eliminated. The vibration damping means shown in that patent differ from the present invention in numerous important respects. For example, the anti-vibration mounting means shown in that patent are not applied to an interference-fitted stator core and support housing assembly. Accordingly, no provision is made in that disclosure for preventing the distortion of a stator core due to its interference with the supporting housing. Moreover, no provision is made in the teaching of that patent for preventing the distortion of a stator core from a desirable predetermined configuration, such as the normally desirable generally cylindrical configuration that the inner diameter of a stator core should have in order to enable it to fit closely and precisely with an associated rotor. In addition, the vibration damping resilient support ribs used in the embodiments disclosed in U.S. Pat. No. 4,145,626 are not pre-stressed or pre-loaded to any apparent significant desired level when the machine is initially manufactured, but rather are mounted in an essentially unstressed condition that is effective to fully preserve the resilience of those ribs for their intended vibration damping purposes when the electrodynamic forces resulting from operation of the machine cause irregular distortions of the stator core as the machine is energized.